In the future, as energy demands rise and fossil fuel supplies decrease, it will become increasingly important to harness the energy of renewable energy sources such as solar energy. Although solar cells are presently capable of harnessing solar energy, the external terrestrial environment presents numerous problems requiring systems to protect solar cells. The solar cell, for example, must be protected from moisture which will degrade cell efficiency and impacts (e.g., from hail, dust, etc.) which may damage or destroy the cell.
To protect solar cells, existing technology encapsulates the solar cell in a "sandwich" structure known as a photovoltaic module. The structure includes upper and lower panels sealed at their perimeters to define a sealed, inner space between the panels. The solar cell is located within the inner space. To effectively protect the solar cell, the photovoltaic module must be able to withstand a number of threats to module integrity including vertical and horizontal shocks while protecting the inner space from moisture penetration that can damage the cells.
There are several approaches to protect against vertical shocks. In a first approach, a thermoplastic strip is positioned underneath the perimeter of the photovoltaic module. An example is U.S. Pat. No. 4,249,519. Panels designed in this manner have been found to fail in a number of situations, such as hail storms.
In a second approach, flexible layered glass panels are employed as the upper panel. An example is U.S. Pat. No. 4,571,446. The problem with this approach is that the bending of the panels in response to vertical shocks may damage the solar cell. This is especially true for thin film solar cells deposited on the lower surface of the upper panel which can be damaged by elongation of the lower surface of the panel during flexing of the panels.
In a third approach, tempered glass is supported by a continuous layer of ethyl vinyl acetate. An example is U.S. Pat. No. 4,625,070. The problem with this approach is that the ethyl vinyl acetate photodegrades over time into a material that adversely affects the operation of the solar cells in the module, thereby decreasing cell efficiency.
To protect against horizontal shocks, it is known to use thermoplastic strips contacting the outer perimeter of the photovoltaic module. Examples are U.S. Pat. Nos. 4,633,032; 4,332,241; 4,266,383; 4,249,519; and 4,003,363. The problem with this approach is that the strips promote penetration of moisture through the perimeter seal into the inner space between the upper and lower panels where the moisture can adversely affect the solar cells. Consequently, there is a need for a device to protect a photovoltaic module against horizontal shocks that also reduces the possibility of moisture penetrating the seal between the panels.
To seal the perimeters of the upper and lower panels, it is known to use sealing structures that incorporate thermoplastic materials such as vinyl strips and various resins. Examples are U.S. Pat. Nos. 4,633,032; 4,249,519; and 4,003,363. Unfortunately, these sealing structures are still susceptible to seal failure, thereby permitting water to penetrate into the space between the upper and lower panels.